Accord Reducing Chemical Arms to Be Signed Today : Military: Carrying out the U.S.-Soviet pact promises to be more difficult than other weapons control accords.

Spurred by the unexpected use of poison gas in the Iran-Iraq War, the United States and the Soviet Union will sign an agreement today to eliminate most of their stocks of chemical weapons, perhaps the most abhorrent killing devices of the 20th Century.

The agreement will be the first international pact since immediately after World War I to control nerve gas and other lethal chemical agents. And it represents a big step from the two nations’ rancorous exchanges over the issue just a few years ago.

The Reagan Administration, for example, once accused the Soviets of sending “yellow rain” chemical weapons to Vietnam for use in Laos and Cambodia. Samples of the “rain,” however, turned out to be feces dropped by bees in mass “cleansing” flights known to occur in the region.

The superpowers hope that the new accord will set an example for other nations and boost ongoing U.N. talks on a proposed global ban of chemical weapons, which about 15 nations now possess and another five or six are trying to develop.

Carrying out the pact, however, promises to be more difficult than enforcing any other arms control measure. Destroying poison gases, usually by burning, must be done very carefully in special facilities, most of which are yet to be built. As little as .001 gram of a deadly nerve gas can be lethal.

The only Soviet facility for eliminating chemical weapons has been closed down after protests by residents near its site on the Volga River. The United States has eight plants under construction. Under the accord, Washington will share destruction technology with the Soviets, who hope that their environmentalists will be calmed by U.S. expertise.

Verification of the agreement also will be extraordinarily difficult. In fact, monitoring procedures are not yet completed, a problem that probably will prevent submission of the pact to Congress for approval until later in the year.

Virtually any plant that produces insecticides, which work on the same principle as nerve gases, can make the lethal substances for war, complicating the task of policing the agreement. Chemical weapons are much simpler to produce than nuclear weapons.

On the other hand, many tons of a chemical weapon are needed for war. One ton would be needed to cover a single mile of battle front, for example, and a stockpile must be at least 1,000 tons to be militarily significant, according to a French study. Special equipment is needed to deliver the weapons and troops need training to use it, all of which would be hard to achieve without detection.

The U.S.-Soviet “executive agreement” provides for some actions to be taken now and for additional steps after approval of a worldwide treaty.

Initially, both sides will cut their chemical arsenals to 5,000 tons each within 10 years, eliminating 80% of current U.S. stocks and at least 90% of Soviet stocks. They also will stop new production of such weapons when the agreement enters into force, probably next year.

After a global chemical weapons treaty is completed, the United States and the Soviet Union will begin further reductions to 500 tons, or 2% of the current U.S. arsenal, over the following seven years. At that time, they will decide whether to destroy the rest.

As a hedge against recalcitrant nations, the Bush Administration wants to hold on to the remaining 2% until all nations capable of making chemical weapons join the worldwide ban. The Soviets have supported proposals to totally eliminate the weapons within 10 years of the global treaty.

The agreement required a compromise by each side, according to Charles C. Flowerree, a former U.S. negotiator. The United States agreed to stop production, which the Soviets wanted, in exchange for Soviet acceptance of the 2% residue.

The United States had resumed production of chemical weapons in 1987 after an 18-year halt. Congress ordered the destruction of existing weapons by 1997 because they are obsolete and dangerous but the Pentagon believed that it still needed some weapons for deterrence purposes.

The Soviets, in contrast, declared a unilateral halt in production in 1987. That move did not stop U.S. plans to produce modern, binary chemical weapons, however, so Moscow pursued that aim, successfully, through the negotiations.

Executive agreements must be approved by a simple majority of both houses of Congress, in contrast to formal treaties that require a two-thirds majority in the Senate, and the new accord seems certain to be passed. But the verification provisions probably will draw conservative fire because of some loopholes.

U.S. inspectors must take the word of the Soviets on the size of their current stockpile, for example. There is considerable dispute among U.S. agencies on the size of the Soviet arsenal. The Pentagon has estimated it at 75,000 tons, but the Soviets say publicly that it is under 50,000 tons and reportedly have told U.S. officials that it is about 40,000 tons.

On-site inspectors will only be able to police destruction of the weapons and thus measure how much is destroyed. But some weapons above the permitted ceiling could be held back secretly if the original arsenals are larger than declared.

CHEMICAL WEAPONS AGREEMENT BACKGROUND

President Bush and Soviet President Gorbachev are expected to sign an accord calling for substantial cuts in chemical weapons. The existing U.S. arsenal is believed to be 25,000 to 30,000 tons, while the Soviets say they have an existing stockpile of less than 50,000 tons.

POINTS OF AGREEMENT

Existing chemical weapons stocks will be reduced to 5,000 tons each over 10 years.

Production of new chemical weapons will be halted when the agreement takes effect.

The two countries will work for approval of a worldwide ban as soon as possible, after which they will cut their arsenals to 500 tons each over a period of seven years.

Elimination of remaining stocks will be considered after that. The U.S. wants to keep residual stocks until all nations capable of making chemical arms join a global ban, while the Soviets want total elimination.

Each nation has the right to conduct on-site verification of weapons destruction. The Soviets oppose a firm destruction schedule because their only destruction plant, just built, cannot open because of environmental objections.

HISTORY

Chemical weapons were used extensively in World War I. Widespread revulsion led to approval of the 1925 Geneva Protocol banning their use in war. Chemical weapons were not deployed on major fronts in World War II, but they were heavily used during the Iran-Iraq War of the past decade.

KINDS OF WEAPONS

Nerve Agents: Related to modern pesticides, they inhibit the action of an enzyme essential to the nervous system, causing paralysis and heart failure.

Blister Agents: Mustard gas and related products burn body surfaces, producing painful skin wounds. If inhaled, they can kill by blistering the lungs.

Blood Agents: Hydrogen cyanide and cyanogen chloride, when inhaled, block the ability of blood cells to convey oxygen.

Toxins: These poisonous substances are extracted from living creatures, such as saxitoxin from shellfish and mycotoxins from fungus.

Sources: U.S. Arms Control and Disarmament Agency, Arms Control Assn., Congressional Quarterly.